Hi. I was driving my boat, suddenly the rpm increased slightly. On the way home it was difficult to keep the boat on plane because the engine reved without the prop doing the same. What could it be? 502 MPI, Bravo One drive, solid hub prop. Could it be the steel cone clutch that is slipping? The forward and reverse gears seem to work.

2- Ideas:

Coupler splines
clutch assy.

check the coupler

Hi. If it was the coupler, wouldn´t the prop stop completely? There are no noises and no smoke just the slip when advancing the throttle beyond half the travel.

Some of the Mirage props have plastic cavitation plugs on the sides that are supposed to allow cavitation if it is desired. One of these may have come out, if so equipped. We tried taking them out on a friend's boat, and couldn't even get the boat on plane.

Just something simple to check before you tear into the drive.

Thanks Budman, unfortunately there are no cavitation plugs. Could it be the shift cable that is out of adjustment? Or is that just wishful thinking?

if it were slipping in and out of gear at hal throttle you'd know it it'd bang like hell when it went back into gear, Don't take this the wrong way but are you sure its not a dive trim issue? bad reading on trim indicator?

I stays in gear , but it revs up without gaining speed. I agree it acts like it was ventilating. I trimmed it down all the way to be sure it was not a trim issue.However, I did that based on the trim instrument. I did not look over the transom, but I will just to make sure. To be continued......

Sounds like cavitation/ventilation to me...The alternatives would not leave you guessing, as mentioned. When couplers go, they go...period! A clutch failure is also unlikely if operation of the drive at other speeds is still smooth...

Are you sure you have a solid hub prop, because that's exactly what happens when a hub starts to slop.